Chemical imaging fiberscope

ABSTRACT

A fiberscope device is disclosed which is suitable for video imaging, laser Raman spectroscopy and laser Raman spectroscopic (i.e. chemical) imaging. The fiberscope design minimizes fiber background interference arising from the laser delivery fiber optic and the coherent fiber optic light gathering bundle while maintaining high light throughput efficiency through the use of integrated spectral filters. In the fiberscope design, the laser delivery fiber optic is offset from the coherent fiber optic light gathering bundle. The laser delivery field is captured entirely by the light gathering field of view of the coherent fiber bundle. The fiberscope incorporates spectral filter optical elements that provide environmental insensitivity, particularly to temperature and moisture. The fiberscope is suited to the analysis of a wide range of condensed phase materials (solids and liquids), including the analysis of biological materials such as breast tissue lesions and arterial plaques, in such a manner to delineate abnormal from normal tissues.

This application claims the benefit of U.S. Provisional Application No.60/144,518, entitled “Chemical Imaging Fiberscope” filed Jul. 19, 1999.

FIELD OF THE INVENTION

The present invention is related to fiberscope probes for spectroscopicand image analysis, and, in particular, to probes useful for both Ramanspectroscopy and Raman chemical imaging.

BACKGROUND OF THE INVENTION

Raman chemical imaging combines Raman spectroscopy and digital imagingfor the molecular-specific analysis of materials. Raman chemical imaginghas traditionally been performed in laboratory settings usingresearch-grade light microscope technology as the image gatheringplatform. However, Raman chemical imaging is applicable to in situindustrial process monitoring and in vivo clinical analysis. Theapplication of chemical imaging outside the research laboratory has beenlimited by the lack of availability of stable imaging platforms that arecompatible with the physical demands of industrial process monitoringand clinical environments. Both industrial and clinical settings oftenrequire compact, lightweight instrumentation suitable for theexamination of remote areas that are inaccessible to conventional Ramaninstrumentation and involve harsh chemicals in hostile environments.

Raman spectroscopy is an analytical technique that is broadlyapplicable. Among its many desirable characteristics, Raman spectroscopyis compatible with samples in aqueous environments and can be performedon samples undergoing little or no sample preparation. The technique isparticularly attractive for remote analysis via the use of opticalfibers. By employing optical fibers as light delivery and collection,the light source and light detector can be physically separated from thesample. This remote attribute is particularly valuable in sensing andanalysis of samples found in industrial process environments and livingsubjects.

In a typical fiber-optic-based Raman analysis configuration, one or moreillumination fiber-optics deliver light from a light source (typically alaser) through a laser bandpass optical filter and onto a sample. Thelaser bandpass filter allows only the laser wavelength to pass whilerejecting all other wavelengths. This purpose of the bandpass filter isto eliminate undesired wavelengths of light from reaching the sample.Upon interaction with the sample, much of the laser light is scatteredat the same wavelength as the laser. However, a small portion of thescattered light (1 in 1 million scattered photons) is scattered atwavelengths different from the laser wavelength. This phenomenon isknown as Raman scattering. The collective wavelengths generated fromRaman scattering from a sample are unique to the chemistry of thatsample. The unique wavelengths provide a fingerprint for the materialand are graphically represented in the form of a spectrum. The Ramanscattered light generated by the laser/sample interaction is thengathered using collection optics which then direct the light through alaser rejection filter which eliminates the laser light, allowing onlyRaman light to be transmitted. The transmitted light is then coupled toa detection system via one or more collection fiber-optics.

Previously described Raman fiber optic probe devices have severallimitations. First, current fiber-optic-based Raman probes are sensitiveto environmental variability. These devices often fail to functionproperly when the probe is subjected to hot, humid-and/or corrosiveenvironments. Several fundamental differences from current devices havebeen incorporated into the chemical imaging fiberscope design describedhere that address the environmental sensitivity issue. First, an outerjacket that is mechanically rugged and resistant to high temperaturesand high humidity has been incorporated into the fiberscope design.Second, an optically transparent window that withstands harsh operatingenvironments, has been built into the probe at the fiberscope/sampleinterface. Normally, incorporation of a window into a probe wouldintroduce a significant engineering problem. As emitted illuminationlight passes through the window and onto the sample, a portion of thislight is back reflected by the window's inner and outer surfaces. In theprior art, this undesired back reflected light is inadvertentlyintroduced into the collection fibers along with the desired Ramanscattered light. The back reflected light corrupts the quality of theanalysis. This problem is addressed in the current design by carefulengineering of the aperture of the collection bundle taking into accountthe numerical apertures (NA) associated with the collection bundlefibers and collection lenses.

Previous probe designs are also inadequate because of the environmentalsensitivity of the spectral filters that are employed in the devices.The Raman chemical imaging fiberscope design of the current inventionrelies on spectral filter technologies that are remarkably immune totemperature and humidity. Past spectral filters have traditionally beenfabricated using conventional thin film dielectric filter technologywhich are susceptible to temperature and humidity induced degradation inthe filter spectral performance. The spectral filters described in thepresent invention employ highly uniform, metal oxide thin film coatingmaterials such as SiO₂, which exhibits a temperature dependent spectralbandshift coefficient an order of magnitude less than conventionalfilter materials. The improved quality and temperature drift performanceof metal oxide filters imparts dramatically improved environmentalstability and improved Raman performance under extreme conditions oftemperature and humidity.

A final limitation of current probe technologies is that none combinethe three basic functions of the chemical imaging fiberscope: (1) videoinspection; (2) Raman spectral analysis; and (3) Raman chemical imageanalysis, in an integrated, compact device.

Raman chemical imaging integrates the molecular analysis capabilities ofRaman spectroscopy with image acquisition through the use ofelectronically tunable imaging spectrometers. Several imagingspectrometers have been employed for Raman chemical imaging, includingacousto-optical tunable filters (AOTFs) and liquid crystal tunablefilters (LCTFs). For Raman imaging, LCTFs are clearly the instrument ofchoice based on the following demonstrated figures of merit: spatialresolving power (250 nm); spectral resolving power (<0.1 cm⁻¹); largeclear aperture (20 mm); and free spectral range (0-4000 cm⁻¹). AOTFs andLCFPs are competitive technologies. AOTFs suffer from image artifactsand instability when subjected to temperature changes.

Under normal Raman imaging operation, LCTFs allow Raman images ofsamples to be recorded at discrete wavelengths (energies). A spectrum isgenerated corresponding to thousands of spatial locations at the samplesurface by tuning the LCTF over a range of wavelengths and collectingimages systematically. Contrast is generated in the images based on therelative amounts of Raman scatter or other optical phenomena such asluminescence that is generated by the different species locatedthroughout the sample. Since a spectrum is generated for each pixellocation, chemometric analysis tools such as Cosine Correlation Analysis(CCA), Principle Component Analysis (PCA) and Multivariate CurveResolution (MCR) are applied to the image data to extract pertinentinformation.

SUMMARY OF THE INVENTION

To address the need for remote chemical inspection technology, a novelflexible fiberscope device has been developed that is Raman chemicalimaging capable. The design of the Raman chemical imaging fiberscope hasseveral advantages over the prior art. First, metal oxide dielectricfilters are used. These filters are effectively immune to humidity andtemperature changes, in stark contrast to traditional dielectricfilters.

Second, the Raman chemical imaging fiberscope is shrouded in a jacketthat is mechanically rugged. Further, a window is used as an opticallytransparent boundary separating the sample environment from the opticalcomponents in the probe.

Third, an imaging fiber-optic or fiberscope has been incorporated intothe design, thereby making the Raman chemical imaging fiberscope bettersuited for interrogating heterogeneous samples. Visual inspection of thesample surfaces and fluids through the use of imaging fiber optics anddigital imaging sensors make in-situ monitoring simpler to implement.Further, the video capabilities of the fiberscope can be used toposition and focus the sensor. This is especially critical whendeploying Raman sensors in confined environments using robotic systems.

The various aspects of the present invention may be more clearlyunderstood and appreciated from a review of the following detaileddescription of the disclosed embodiments and by reference to theappended drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross section of the distal end of the Raman chemicalimaging fiberscope.

FIG. 2 shows a functional flowchart of pathways for light delivery andcollection through the chemical imaging fiberscope.

FIGS. 3A and B show the bright field images of the exterior and interiorof a bore hole respectively, captured through the chemical imagingfiberscope.

FIG. 4A shows an image of the laser beam projected onto a resolutiontarget images collected through the Raman chemical imaging fiberscope.FIG. 4B shows an image of the resolution target only for comparison.

FIG. 5A shows the simultaneous transmission of white light and laserlight through the laser delivery fiber optic and laser bandpass filter;FIG. 5B shows the transmission bandpass through the laser rejectionfilter and coherent imaging bundle.

FIGS. 6A and B show Raman spectra of a sodium nitride pellet and asodium phosphate solution, respectively, captured through the chemicalimaging fiberscope.

FIG. 7 shows Raman spectra of zirconium oxide collected at roomtemperature and 205° C. through the chemical imaging fiberscope.

FIGS. 8A and B show bright field images of an aspirin tablet collectedthrough the fiberscope under white light illumination conditions. FIG.8C shows a Raman spectrum of the aspirin tablet captured from the boxedregion in FIG. 8B and collected with a dispersive Raman spectrometerunder Raman spectroscopy conditions.

FIG. 9A shows bright field images of a microregion of a tabletcontaining aspirin collected through the fiberscope under white lightillumination conditions. FIG. 9B shows a Raman chemical image of thesame tablet collected through the fiberscope operating under Ramanimaging conditions. FIG. 9C shows representative Raman spectra collectedthrough imaging spectrometer of aspirin and excipient.

DETAILED DESCRIPTION OF THE INVENTION

The Raman chemical imaging fiberscope combines in a single platform alaser beam delivery system to irradiate samples for Raman spectroscopy,an incoherent fiber optic bundle to deliver white light illumination anda coherent fiber bundle suitable for Raman spectral collection, Ramanimage collection and digital video collection.

The distal end of the fiberscope is shown in cross-section in FIG. 1.The external housing 10 surrounds the inner core of the fiberscope. Theouter jacket is mechanically rugged and immune to hostile samplingenvironments. At the distal end of the fiberscope is window 12. Thiswindow is, in the preferred embodiment, composed of quartz, diamond orsapphire and is used as an optically transparent boundary separating thesample environment from the optical components in the probe.

Laser illumination fiber 14 delivers laser illumination to the sample.This light passes through laser bandpass filter 24, which filters outall wavelengths of light other than the specific wavelength of the laserlight transmitted through laser illumination fiber 14. The laserlight/sample interaction generates Raman scattering. The scattered lightis then collected through the end of the fiberscope. It should be notedthat laser bandpass filter 24 is spatially patterned and has opticalcoatings only on the top portion thereof, such that light exiting laserillumination fiber 14 will be filtered, but scattered light entering theend of the probe will not experience any filtering by laser bandpassfilter 24. The portion of laser bandpass filter 24 which receivesscattered light from the sample and transmits it to image collectionbundle 18 is transparent and performs no filtering function.

After passing through laser band pass filter 24, the scattered lightapertured by a spatial filter 28 which acts to restrict the angularfield of view of the subsequent optical system. The scattered light isthen focused by a pair of lenses 22. The light is then passed throughlaser reflection filter 20. This filter effectively filters out lighthaving a wavelength identical to the laser light, which was originallytransmitted onto the sample through laser illumination fiber 14. Afterpassing through filter 20, the light is transmitted back to the imagingapparatus by the image collection bundle 18.

Successful use of the Raman chemical imaging fiberscope depends on theperformance of the spectral filters in humid, elevated-temperatureenvironments. Conventional filters are characterized by the presence ofmicroscale pits and voids. These microstructures absorb water in humidconditions, which cause the thin film matrix to swell and the spectralproperties to change, causing the fiber optic probe to be useless. Inaddition, the coefficients of thermal expansion of traditionaldielectric filter thin films (i.e., ZnS or ZnSe) are relatively large.When exposed to elevated temperatures the traditional filter centerspectral bandpass shifts, rendering them useless unless a mechanism isdevised to rotate the filters and tune them. For example, ZnS has atemperature coefficient of 0.05 nm/° C.

In the preferred embodiment, the filters are metal oxide dielectricfilters of the type manufactured by Corion. Metal oxide filters have lowcoefficients of thermal expansion, and, when exposed to elevatedtemperature environments the thin film materials comprising theFabry-Perot cavities do not exhibit gross variation in thin filmthickness. As a consequence, the metal oxide filters are insensitive totemperature induced spectral changes, primarily peak transmittance. Inaddition, the metal oxide thin film coating is also insensitive tohumidity which enhances the filter performance when exposed to hostileconditions. The metal oxide filters employ SiO₂ as the thin filmmaterial, which exhibits a temperature dependent spectral bandshiftcoefficient of about 0.005 nm/° C.

The imaging fiber optic bundles are preferably high temperatureresistant coherent fiber optic bundles, such as those developed bySchoft Glass. These bundles have the unique property that the polyamidecladding employed for typical coherent fiber bundles is leached away (inacid bath) leaving an all-glass fiber bundle that is flexible and can beoperated at high temperatures up to about 400° C.

Video imaging of the sample is performed by shining white light on thesample. The white light is transmitted via fibers 26. High qualityimaging optics are employed to provide the ability to visually inspectthe sample area and to obtain Raman chemical images. Collection lenses22 focus an image of the sample on the image collection bundle 18. Thecoherent image collection bundle 18 independently captures white lightand Raman scattered photons from the sample surface. The Raman chemicalimaging fiberscope provides remote real-time video imaging of the samplewhen the white light is directed through the image collection bundle 18to a video CCD. Live video capability assists insertion of thefiberscope and allows visual inspection of the sample area inpreparation for spectroscopic analysis. White light for video imagingcan be produced by a high power (300 W) Xe lamp.

The Raman scatter is collected through the coherent image collectionbundle 18 used to capture the live video. However, laser rejectionfilter 20 is used to suppress generation of SiO₂ Raman background withinthe image collection bundle 18. As shown in FIG. 2, once collected, theRaman scatter can be diverted in two directions. When sent to adispersive spectrometer, the Raman chemical imaging fiberscope providesconventional Raman spectral information. The Raman scatter can also bedirected through a liquid crystal tunable filter (LCTF) imagingspectrometer onto a sensitive digital CCD. Because the Raman image ismaintained through the image collection bundle 18, high quality Ramanchemical images can be collected across the fiberscope field of view.

FIG. 2 shows a functional diagram of the Raman chemical imagingfiberscope system. Laser light illumination and white light videoilluminations are represented by reference numbers 1 and 2 respectively.These lights enter the fiberscope and are transmitted out the end of thescope to the sample. The Raman spectrum 3, the Raman image 4 and thelive video image 5 are transmitted back into the end of the fiberscope.Raman spectrum 3 and Raman image 4 are delivered to processing apparatuswhich effectively displays the desired information, as described above,while live video image 5 is directed to a monitor for viewing by theuser.

FIG. 3 shows the imaging capabilities of the Raman chemical imagingfiberscope. FIGS. 3A and 3B shows a high fidelity image of the exteriorand interior, respectively, of a bore hole. These are bright fieldimages using white light illumination, which show the video performanceof the Raman chemical imaging fiberscope. Overall, the Raman chemicalimaging fiberscope has a wide field of view and superb image quality.

The video performance of the Raman chemical imaging fiberscope wasevaluated by recording a digital image of a USAF 1951 resolution target.The target was illuminated with a diffuse Xe arc lamp source. The outputof the Raman chemical imaging fiberscope was optically coupled to acolor CCD video camera and bright field images were digitized using adigital frame grabber. To determine the laser spot position anddimension, a diode pumped Nd:YVO⁴ laser doubled to produce 532 nm light(Millenia II, Spectra Physics) was injected into the laser deliveryfiber. The resultant laser spot was projected onto the resolution targetsubstrate at a nominal working distance of 1 cm.

FIG. 4 shows resolution target images collected through the Ramanchemical imaging fiberscope when back-illuminated with a diffuse Xesource. In FIG. 4A, a 532 nm laser beam was focused into the laserdelivery fiber using a high efficiency laser to fiber optic coupler andan image of the laser spot was recorded on a diffuse target superimposedon the resolution target. At a working distance of 1 cm the spot seennear the center of the target image is approximately 2.5 mm in diameter.The laser spot size can be controlled through laser to fiber opticinjection strategies and via working distance to the sample. Forcomparison, FIG. 4B shows the digital image of the USAF resolutiontarget.

As previously described, high performance, environmentally resistantspectral filters are incorporated into the distal end of the flexibleRaman chemical imaging fiberscope. Room temperature spectra wereacquired to measure the out of band rejection efficiency of thefiberscope using combinations of white light and laser light. Roomtemperature spectra were acquired to measure the 532 nm laser rejectionefficiency during fiberscope collection. Laser rejection is required forthe observation of the weak Raman signal and to prevent the inherentRaman scatter of the collection fiber. Xenon light was sent into thecollection end of the fiberscope. The output from the viewing end of thefiberscope was measured using a dispersive spectrometer.

FIG. 5 shows transmission spectra collected through the Raman chemicalimaging fiberscope. FIG. 5A shows the transmission bandpass through thelaser delivery fiber optic under simultaneous Xe white light and 532 nmlaser light illumination. From this spectrum, it is apparent that theincorporated bandpass filter sufficiently passes 532 nm light whilecutting off transmission above 140 cm⁻¹ red-shifted from the laser line.FIG. 5B shows the transmission bandpass through the filter incorporatedwithin the coherent fiber bundle. It is apparent that the incorporatednotch filter sufficiently rejects 532 nm light while passing light above200 cm⁻¹ red-shifted from the laser line.

Dispersive Raman spectra of sodium nitrate and sodium phosphate inaqueous solution collected with the Raman chemical imaging fiberscopeare presented in FIG. 6. The sodium nitrate Raman spectrum in FIG. 6Areveals the characteristic nitrate band at 1065 cm⁻¹. Note the highsignal to background ratio (S/B) and the absence of fiber optic Ramanbackground. In FIG. 6B, the phosphate bands at 945 cm⁻¹ and 995 cm⁻¹ canbe seen.

Room temperature Raman spectra of a sodium nitrate pellet, was collectedto assess the Raman collection performance of the Raman chemical imagingfiberscope. The viewing end of the fiberscope was coupled to adispersive Raman spectrometer. Illumination of the sodium nitrate pelletwas provided by injecting laser light into the laser delivery fiber.

High temperature Raman spectra of zirconium oxide were also collected. Afurnace was used to heat the sample and distal end of the Raman chemicalimaging fiberscope. A thermocouple was used to monitor the temperatureat the distal end of the fiberscope. The viewing end of the fiberscopewas coupled to a dispersive Raman spectrometer. Illumination of thezirconium oxide pellet was provided by injecting laser light into thelaser delivery fiber of the Raman chemical imaging fiberscope.

FIG. 7 shows two zirconium oxide spectra—one collected at roomtemperature (27° C.), the other at 205° C. The Raman features are stilldiscernable in the high temperature spectrum. There is an increase inthe overall intensity of the background signal (thermal background) andin the relative intensities of the peaks. Of note, both spectra showRaman features to well within 200 cm⁻¹ of the laser line.

Raman chemical image data was collected from an over the counterpharmaceutical tablet containing aspirin (Alka Seltzer, Bayer). Theimage from the viewing end of the fiberscope was focused onto a CCDcamera and an LCTF was inserted into the optical path. Dispersivespectroscopy revealed that the tablet excipient had a Raman band at 1060cm⁻¹. Since this is close to the 1044 cm⁻¹ Raman band of aspirin, thesetwo peaks were used for chemical image analysis. A CCD image wascollected every 9 cm⁻¹ while the LCTF was tuned from 1000 cm⁻¹ to 1110cm⁻¹.

Images of the tablet collected through the fiberscope using ambientlight can be seen in FIGS. 8A and 8B. The box in FIG. 8B shows theregion from where the Raman spectrum in FIG. 8C was acquired. FIG. 8Cshows a dispersive Raman spectrum dominated by aspirin (acetylsalicylicacid). The box shaded in gray represents the spectral range that wassampled to generate Raman chemical images (see FIG. 9).

The multivariate technique cosine correlation analysis (CCA) was appliedto Raman chemical image data using Chemimage software, produced by theassignee of this invention, Chemicon. CCA is a multivariate imageanalysis technique that assesses similarity in chemical image data setswhile simultaneously suppressing background effects when performed inconjunction with normalization of each linearly independent Ramanspectra contained in the image dataset. CCA assesses chemicalheterogeneity without the need for extensive training sets. CCAidentifies differences in spectral shape and effectively providesmolecular-specific contrast that is independent of absolute intensity.

FIG. 9 displays the Raman chemical imaging results from the aspirintablet. FIG. 9A is a bright field image of the sampled area capturedthrough the Raman chemical imaging fiberscope. FIG. 9B is a grayscaleRaman chemical image generated using CCA with the brightest regionsshowing the aspirin component at 1044 cm⁻¹ and the darker regionsshowing the excipient component (calcium carbonate) collected at 1060cm⁻¹. FIG. 9C shows LCTF Raman spectra from regions 1 (localizedaspirin) and 2 (excipient), respectively.

In summary, the Raman chemical imaging fiberscope is the firstfiberscope technology which incorporates all of the following: laserdelivery, white light illumination, video collection, Raman spectralcollection and LCTF-based Raman chemical imaging capability within acompact device (the distal end outside diameter of the flexiblefiberscope is only 2 mm). The Raman chemical imaging fiberscope isenvironmental resistant and can be used in a variety of hostile andconfined environments over a range of operating temperatures andhumidities. Due to its compact dimensions and rugged design, the Ramanchemical imaging fiberscope is well suited to in situ industrialmonitoring and in vivo clinical applications.

Although the invention was described in the context of a Ramanfiberscope probe, the present invention offers the ability to performother chemical (spectroscopic) imaging techniques such as near infra-redand luminescence chemical imaging.

The present invention has been described in relation to particularembodiments which are intended in all respects to be illustrative ratherthan restrictive. Alternative embodiments will become apparent to thoseskilled in the art to which the present invention pertains withoutdeparting from its spirit and scope. Accordingly, the scope of thepresent invention is defined by the appended claims rather than theforegoing description.

1. A method of imaging and collecting Raman spectra from a sample, themethod comprising: transmitting laser light of a specific laserexcitation wavelength from a first source to a sample via one or morelaser illuminating fibers; positioning a first portion of a spectralfilter between said one or more laser illumination fibers and saidsample for transmitting said laser light of said specific laserexcitation wavelength and rejecting light of other wavelengths;positioning a second portion of the spectral filter between said sampleand a plurality of collection fibers for transmitting wavelengths oflight other than said specific laser excitation wavelength; andreceiving light scattered from said sample via said plurality ofcollection fibers; wherein the spectral filter is spatially patternedinto the first portion for filtering said laser light and into thesecond portion for transmitting light scattered or reflected by saidsample to said plurality of collection fibers.
 2. The method of claim 1wherein said plurality of collection fibers are arranged in a coherentbundle.
 3. The method of claim 1 wherein at least one of said first orsecond portions of the spectral filter exhibit environmentalinsensitivity to temperature and humidity.
 4. The method of claim 1further comprising positioning one or more lenses between said sampleand said plurality of collection fibers.
 5. The method of claim 1wherein said first or second portions of the spectral filter arecomposed of a filter type selected from a group consisting ofdielectric, holographic and rugate spectral filters.
 6. The method ofclaim 1 further comprising positioning a spatial filter between saidsample and said collection fibers for controlling an angular field ofview of said collection fibers.
 7. The method of claim 1 furthercomprising: holding the distal end of a housing in proximity to saidsample wherein said housing encloses said spectral filter, said one ormore laser illuminating fibers, and said plurality of collection fibers;directing the output of the collection fibers under white lightillumination conditions to a live video camera via a first link;directing the output under laser illumination conditions to a Ramanspectrometer via a second link; directing the output under laserillumination conditions to a Raman chemical imaging spectrometer anddetector via a third link.
 8. The method of claim 1 wherein a housingencloses said spectral filter, said one or more laser illuminatingfibers and said plurality of collection fibers.
 9. The method of claim 8wherein a window is disposed at the distal end of said housing.
 10. Themethod of claim 9 wherein said window is composed of a material selectedfrom a group consisting of quartz, diamond and sapphire.
 11. The methodof claim 1 further comprising selectably transmitting white light from asecond source to said sample with a plurality of white lightillumination fibers.
 12. The method of claim 11 wherein said pluralityof collection fibers are arranged in a coherent bundle.
 13. The methodof claim 12 wherein at least one of said first or second portions of thespectral filter exhibit environmental insensitivity to temperature andhumidity.
 14. The method of claim 13 further comprising positioning oneor more lenses between said sample and said plurality of collectionfibers.
 15. The method of claim 11 wherein a housing encloses saidspectral filter, said one or more laser illuminating fibers, saidplurality of white light illumination fibers and said plurality ofcollection fibers.
 16. The method of claim 15 wherein a window isdisposed at the distal end of said housing.
 17. The method of claim 16wherein said window is composed of a material selected from a groupconsisting of quartz, diamond and sapphire.
 18. The method of claim 11wherein said spectral filter exhibits environmental insensitivity totemperature and humidity.
 19. The method of claim 11 further comprisingpositioning a spatial filter between said sample and said collectionfibers for controlling an angular field of view of said collectionfibers.
 20. A method of imaging and collecting Raman spectra from asample with a chemical imaging spectroscope, the method comprising:transmitting laser light of a specific laser excitation wavelength froma first source to a sample via one or more laser illuminating fibers;positioning a first portion of a spectral filter between said one ormore laser illumination fibers and said sample for transmitting saidlaser light of said specific laser excitation wavelength and rejectinglight of other wavelengths; positioning a second portion of the spectralfilter between said sample and a plurality of collection fibers fortransmitting wavelengths of light other than said specific laserexcitation wavelength; positioning a spatial filter between said sampleand said collection fibers for controlling an angular field of view ofsaid collection fibers; positioning one or more lenses between saidsample and said plurality of collection fibers; and receiving lightscattered from said sample via said plurality of collection fibers;wherein the spectral filter is spatially patterned into the firstportion for filtering said laser light and into the second portion fortransmitting light scattered or reflected by said sample to saidplurality of collection fibers.
 21. A method of illuminating andcollecting light from a sample, the method comprising: transmittinglaser light of a specific laser excitation wavelength from a firstsource to a sample with one or more laser illuminating fibers via afirst optical path; transmitting white light from a second source tosaid sample with a plurality of white light illumination fibers via asecond optical path; receiving light scattered or reflected from saidsample with said plurality of collection fibers; transmitting saidscattered or reflected light to an imaging apparatus via a third path;wherein said one or more laser illumination fibers, said plurality ofwhite light illumination fibers, said plurality of collection fibers aredisposed in a housing wherein said first optical path is different fromsaid second optical path and wherein said first and third optical pathseach include a spectral filter.
 22. The method of claim 21 wherein saidfirst optical path comprises said laser illumination fibers, a firstportion of a spectral filter, and a window disposed at the distal end ofsaid housing.
 23. The method of claim 22 wherein said second opticalpath comprises said white light illumination fibers and said window. 24.The method of claim 23 wherein said third optical path comprises saidwindow and a second portion of said spectral filter.
 25. The method ofclaim 24 further comprising filtering said laser light with said firstportion of the spectral filter; wherein said first portion of saidspectral filter is spatially patterned for filtering said laser lightand said second portion of the spectral filter is transparent fortransmitting light scattered or reflected by said sample to saidcollection fibers.
 26. The method of claim 25 wherein said third opticalpath comprises said window, said second portion of said spectral filter,a spatial filter, a lens, a reflection filter, and said collectionfibers.
 27. The method of claim 21 wherein said first and second opticalpaths are each different from said third optical path.
 28. The method ofclaim 21 wherein a first portion of said spectral filter is spatiallypatterned for filtering said laser light and a second portion of saidspectral filter is transparent for transmitting light scattered orreflected by said sample to said collection fibers.
 29. The method ofclaim 21 wherein said spectral filter exhibits environmentalinsensitivity to temperature and humidity.
 30. The method of claim 21wherein said spectral filter is composed of a filter type selected froma group consisting of dielectric, holographic and rugate spectralfilters.
 31. The method of claim 21 wherein said plurality of collectionfibers are arranged in a coherent bundle.
 32. The method of claim 21further comprising: disposing one or more lenses in said third opticalpath.
 33. The method of claim 21 wherein a window is disposed at adistal end of said housing.
 34. The method of claim 33 wherein saidwindow is composed of a material selected from a group consisting ofquartz, diamond and sapphire.
 35. The method of claim 21 wherein saidimaging apparatus comprises a spectrometer.
 36. The method of claim 35wherein said spectrometer is a Raman spectrometer.
 37. The method ofclaim 21 wherein said imaging apparatus includes a tunable filter. 38.The method of claim 37 wherein said tunable filter is a liquid crystaltunable filter.
 39. The method of claim 21 further comprising producinga Raman image of said sample.
 40. The method of claim 21 furthercomprising producing a chemical image of said sample.
 41. The method ofclaim 21 wherein said imaging apparatus comprises a charge-coupleddevice.
 42. The method of claim 41 wherein said charge-coupled device isa video charge-coupled device.